Tim Cook frequently says he's 'bullish' on China, but one analyst now says it's 'doubtful' that Apple can make a comeback there

Apple CEO Tim Cook bows at the opening ceremony of the fourth World Internet Conference in Wuzhen Reuters

China is Apple's second biggest market after North America.

But Apple's Chinese iPhone sales peaked in 2015.

New research from UBS suggests a comeback is "doubtful."

Apple CEO Tim Cook frequently says he's "bullish" on China, but one analyst now says it's "doubtful" that Apple can make a comeback on the mainland.

iPhone sales peaked in China in 2015, powered by a "super cycle" partially driven by the increased screen sizes on the iPhone 6 and iPhone 6 Plus.

But they've been down since then, UBS analyst Steven Milunovich wrote in a note on Monday. "With Hong Kong shrunk and mainland China fairly flat, we no longer see China as a driver of significant iPhone growth," he wrote.

Looking to the future, Milunovich writes that Apple investors can expect flat sales and little long-term growth from Apple's 2nd biggest market, which accounts for 19% of Apple's total iPhone shipments.

Milunovich sees three primary reasons for Apple's malaise in China:

"We think it's doubtful China returns to its 2015 peak as local brands have caught up and upgrade cycles are lengthening; we expect a flattish market, give or take a few points of growth depending on the overall market and product cycle"

"Apple's brand remains strong at the high end, with iOS an important differentiator. Although Apple's fate in China is better than Samsung's, we believe it will be an uphill battle against a maturing market and continued local competition"

"The overall China market appears to be weakening though Apple's share has stabilized and started to improve in Dec and March. iPhone X success has been limited by its high price at 8,000 RMB"

Part of the issue is that Apple only really addresses the high-end of the market, so in smaller, less rich cities, it can have little to no presence. And on the high-end, it faces fierce competition from Chinese giant Huawei. In China, smartphone brands tend to use live "promoters" to sell their phones, but Apple doesn't have nearly as many as companies like Oppo, Vivo, and Huawei.

UBS didn't change its price target from $190 ahead of Apple's earnings on May 1.

Still, Apple's may have some additional branding magic, even in China, that's hard to put into a financial model.

"Furthermore, we've heard that the Chinese consumer appreciates the story of the company — the turnaround under Steve Jobs — as much as do American consumers," Milunovich wrote.